H2s modified cracking of naphtha

ABSTRACT

IN A PROCESS FOR CRACKING A PETROLEUM DERIVED NAPHTHA HAVING A BOLING RANGE OF 90 TO 400*F. AND A SPECIFIC GRAVITY OF 0.65 TO 0.78 TO ALKENES AND ALKANES; THE INSTANT INVENTION RELATES TO AN IMPROVEMENT COMPRISING ADMIXING ABOUT 1.0 TO 35 PARTS BY WEIGHT OF H2S (OR AN AMOUNT OF A COMPOUND WHICH YIELDS AN SH RADICAL IN HE CRACKING ENVIRONMENT SUFFICIENT TO YIELD THAT AMOUNT OF H2S) PER 100 PARTS BY WEIGHT OF ALKANE AND H2S (OR A PRECURSOR THEREOF) IN THE MIXTURE CONSISTING ESSENTIALLY OF H2S (OR THE PRECURSOR THERETO) AND THE NAPHTHA TO BE CRACKED, AND THEN PASSING THE RESULING MIXTURE THROUGH A REACTOR MAINTAINED AT A TEMPERATURE O ABOUT 1100* F. TO ABOUT 2000*F. WITH A RESIDENCE TIME OF ABOUT 0.25 TO ABOUT 2.0 SECONDS AND A PRESSURE OF ABOUT 0 TO ABOUT 65 P.S.I.G. STEAM IS ALSO EMPLOYED.

US. Cl. 260-683 R 7 Claims ABSTRACT OF THE DISCLOSURE In a procses forcracking a petroleum derived naphtha having a boiling range of 90 to 400F. and a specific gravity of 0.65 to 0.78 to alkenes and alkanes; theinstant invention relates to an improvement comprising admixing about1.0 to 35 parts by weight of H 8 (or an amount of a compound whichyields an SH radical in the cracking environment sufficient to yieldthat amount of H 5) per 100 parts by weight of alkane and H 8 (or aprecursor thereof) in the mixture consisting essentially of H 8 (or theprecursor thereto) and the naphtha to be cracked, and then passing theresulting mixture through a reactor maintained at a temperature of about1100 F. to about 2000 F. with a residence time of about 0.25 to about2.0 seconds and a pressure of about 0 to about 65 p.s.i.g. Steam is alsoemployed.

BACKGROUND OF THE INVENTION This invention relates to an improvement inthe cracking of naphtha.

Tremendous quantities of lower alkenes are used and needed by modernchemical process industries. Thus, huge quantities of propylene arepolymerized to polypropylene and are employed to produce acrylonitrile,cumene, isopropanol, plasticizer alcohols, propylene oxide, oxoalcohols, and other chemicals. Lower alkenes are much used to alkylatearomatic compounds and to alkylate paraflins to form high octanecomponents of motor fuel.

A considerable need exists for improved methods of producing suchalkenes which are used and needed in huge and ever increasingquantities. In particular, it is anticipated that the need for propylenewill greatly increase in the near future.

One means for obtaining such lower alkenes is by cracking naphthaderived from petroleum. Any improvement in such a cracking processwhereby the yield of alkenes is improved or whereby the relativeselectivity of propylene to ethylene is improved is of considerablebenefit to the industry and constitutes a significant advance in theart.

OBJECTS OF THE INVENTION One object of the invention is to provide animprovement in the process for cracking naphtha to produce alkeneswhereby the selectivity to the alkene product or the alkene producthaving the greater number of carbon atoms is increased.

Another object of this invention is to provide an improvement in theprocess for cracking naphtha whereby the conversion to alkenes isimproved.

These and other objects and advantages will appear from the followingdescription of the embodiments of the invention, and the most novelfeatures will be particularly pointed out hereinafter in connection withthe appended claims.

SUMMARY OF THE INVENTION In one aspect, this invention discloses animprovement in a process for cracking naphtha having a boiling range of90 to 400 F. and a specific gravity of 0.65 to 0.78 to alkenes andalkenes; wherein the improvement comprises United States Patent 0admixing about 1.0 to 35 parts by weight of H S (or an amount of acompound which yields SH radicals in the cracking environment sufiicientto yield that amount of H S) per 100 parts by weight of H 8 (or theprecursor thereto) with the naphtha to be cracked to form a mixturecomprising H 8 (or a precursor thereof) and the naphtha, and thenpassing the mixture through a reactor maintained at a temperature of1100 F. to about 2000 F. with a residence time of about 0.25 to about2.0 seconds, and a pressure of about 0 to about 65 p.s.i.g.

DESCRIPTION OF THE PREFERRED EMBODIMENTS This invention is based uponthe discovery that introduction of H 8 into the reaction environment ofcertain naphtha cracking reactions in the quantities and under theconditions specified increases conversion and increases the selectivityto, and thereby the production of, alkene reaction products having agreater number of carbon atoms in preference to alkene reaction productshaving a lesser number of carbon atoms. Thus, addition of H 8 to areaction environment wherein naphtha is cracked increases conversion andthe proportion of propylene to ethylene produced. Particularly desirableresults are obtained when steam and H S are concurrently employed.

The naphtha which is cracked according to the process of this inventioncan include any naphtha product having the following properties:

Boiling range -400 F. (D-86). Specific gravity 0.65-0.78.

It is presently preferred to employ a highly paraflinic naphtha derivedfrom petroleum.

The mixture comprising naphtha and H 8 (or a precursor thereof) ispassed to the cracking environment at a pressure of about 0 to about 65p.s.i.g. for a residence time of about 0.25 to 2.0 seconds. If theresidence time is too long, particularly at relatively low pressure,undesirable side reactions occur which militate against the beneficialeffect of adding H S (or a precursor thereto) to the naphtha to becracked.

Preferably, the cracking conversion is conducted continuously. When thecracking conversion is conducted continuously, a gas hourly spacevelocity of about 400 to about 22,000 cc. of gaseous feed volume per cc.of reactor volume per hour at STP (standard temperature pressure) ismost preferably employed. At significantly higher space velocitiesinsufficient reaction occurs to be commercially desirable, and atsignificantly lower space velocities an undue amount of deleterious sidereactions occur.

The reaction environment is often preferably maintained at a temperatureof about 1300 to about 1800" F. Below 1100 F., insufficient conversionoccurs, and above 2000 F, undesirable side reactions occur. The rangebetween 1300 and 1800 F. is the most commercially feasible regionwherein side reactions are minimal but adequate conversion is yetobtained. Still more preferably, the improved cracking conversion isoptimumly conducted at a temperature of about 1400 to 1700 F. when thepreferred naphthas are employed as feedstock.

It is often advantageous to employ the shorter residence times of theinvention when the higher reaction temperatures are employed in order toavoid side reactions which militate against the beneficial effects ofemploying H 3 (orda precursor thereof) in admixture with the naphtha feeAccording to the improvement in the cracking of naphtha of thisinvention, often, about 1.0 to 35 parts by weight of H 8 per parts byweight of the naphtha plus 'I-I S of the feed passed to the crackingreactor are employed. Levels of H 8 below about 1.0 parts by weight arenot effective, and levels above about 35 parts by weight are noteconomical. Often, the feed mixture consists essentially of naphtha andH 5, or in lieu of all or part of the H 8, an equivalent amount of acompound which yields H 8 in the cracking environment. Steam should alsobe employed to mitigate coking.

More preferably, about 2.0 to 20 parts by weight of H 5 (or an amount ofa compound which yields H 5 in the cracking environment sufficient toyield that amount of H 8) per 100 parts by weight of H S (or a precursorthereof) plus the naphtha to be cracked are employed. Such levels aremost commercially feasible. Examples of materials which yields H 8 inthe cracking environment include: mercaptans, mercaptides, thioethers,carbon disulfide, ammonium sulfide, polysulfides such as disulfide oils,sulfur, and the like. Essentially any substance which will yield H 8under the reaction conditions specified otherwise can be employed inlieu of any proportion of the H 8 specified. Which compounds will yieldH 8 under the cracking environment specified are well known to the artor can readily be determined by simple experiment not amounting toinvention. Mixtures of H 8 and an in situ H 8 precursor can be employedif desired.

Gaseous diluents which are substantially entirely inert to the reactionenvironment can be employed if desired. Some examples of such diluentsinclude: nitrogen, helium, neon, steam, methane, ethylene, and the like.A purpose of the diluent is to lower the partial pressure of thehydrocarbon and to minimize coking. Generally less than 1 part ofdiluent per part of feed is suitable.

Steam should be employed to mitigate coking. About 0.5 to 0.75 pound ofsteam per pound of naphtha charged is most suitable.

The H 8 (or precursor thereof) can be admixed with the naphtha and withthe other components of the feedstock, if any, by any means heretoforeknown to the art for admixing fluids. Often, a conventionalproportionator is advantageously employed.

Often the improved cracking process of the instant application isadvantageously conducted in a reaction chamber which is packed with asuitable particulate packing material which can be, but is not limitedto, a heterogeneous catalytic material. Examples of suitable particulatepacking materials include: alumina, kaolin, magnesium oxide, silicates,and the like. Suitable packing material for a packed bed often has thegreatest dimension of particles in the range of inch to inch. Also,presently preferred is a packing material comprising particulate aluminahaving a particle size of about 70 to 400 U .S. sieve employed as afluidized bed.

The H 8 (or precursor thereof) of the instant invention is believed tofunction as a reaction directing agent or catalyst. Thus, the eifectnoted differs from mere metal or catalyst passivation. The system of theinstant invention is a homogeneous system wherein reaction is efiectedupon contact of the gaseous H 8 molecules plus generated radicals andthe gaseous naphtha molecules plus generated radicals.

The following examples are presented so that the invention can be moreclearly understood. These examples should not be interpreted as limitingthe invention.

4 EXAMPLE 1 A cracking feedstock was prepared by admixing 50 weightpercent Kuwait light distillate and Kuwait natural gasoline. Chemicalanalysis of the mixture indicated that the molecular weight ranged fromC to C hydrocarbons. Results of ASTM distillation and gas chromatography of the mixture are given in the following Table I. As indicated inthe table, the feedstock has a boiling point range which isrepresentative of naphthas.

TABLE I AS'IM method Test Results D4298- Specific gravity at 60 F./60 F0. 6849 D4298. API gravity at 60 F 75. 1. D-86. Distillation:

0. initial boiling point 42 C. at which 2 volume percent recovered. 46C. at which 5 volume percent recovered--- 50 C. at which 10 volumepercent recovered.. 54 C. at which 20 volume percent recovered. 57 C. atwhich 30 volume percent recovered. 62 C. at which 40 volume percentrecovered. 68 C. at which 50 volume percent recovered- 77 C. at, which60 volume percent; recovered- 9 C. at which volume percent recovered. 10C. at which 80 volume percent recovered. 12 0. at which volume percentrecovered. 135 C. at which volume percent recovered. 14 C. final boilingpoint 15 Percent volume recovery at 70 0..... 4 Percent volume recoveryat 0.... 6 Percent volume recovery at 140 C 91. 5 Percent volumeresidue. 1. 0 Percent volume ioss.--... 1. 0

D4266- Total sulfur, wt. percent 0. 028 D-323. Reid vapor pressure,lb./sq. in- 8. 5 Color LP. (Lovinbond 18 cell) 0.25

D-156--- Color (Seybolt) Butanes, percent volume- Lead content,parts/billio 13-1319. Hydrocarbon types (FIA)Aromatics/olefins/saturates 4.1/0/95.Q

Chromatographic analysis, approximate Wt. percent Compounds:

H35. 2. 7 I- 3. 9 GIS. 18. 7 C 8 15. 5 Gas 47. 6 C S. 9.2 "Ram one 1. 89Toluene. 0. 80 Xylenes- Trace A tube reactor fabricated of stainlesssteel having an internal diameter of 0.305 inch and a reaction length of2 feet was continuously charged with the above feedstock, with steam,and with a hydrogen sulfide precursor in the form of a 22 percent byweight aqueous solution of ammonium sulfide (except in the control runs)under conditions and with results as indicated in the following TableII. Pressure ranged from 15 to 18 p.s.i.g. Contact time ranged from 0.23to 0.30 second. Approximately 0.75 pound of steam was employed for eachpound of naphtha charged.

TABLE II Run number Na hth feed to, 259 282 270 273. 1 268. 6 276. 0262. 7 267. 1

ste m fe ed rat: 174. 4 214 169. 6 165. 1 166. 7 214 169. 1 212. 0

(NH4)2S solution feed rate, g [hr 43. 6 0 42. 4 43. 9 44. 3 0 44. 9 0

Furnace temperature, C 845 848 860 890 930 940 9.65 970 Total feed rate,l./h1'-- 616. 8 594. 9 605. 7 615. 9 640. 1 623. 1 678. 9 661. 5

Wt 1. .9.? 5. 3 5. 5 6. 9 8. 5 10. 3 13. 2 l4. 9 12. 8 Cl! 7. 8 10. 0 8.6 l0. 7 13. 6 21. 1 18. 1 22. 4 (QT-h 4. 7 2. 8 5. 9 6. 2 6. 0 3. 9 5. 93. 3 (HR- 9. 4 9. 2 11. 1 12. 5 13. 7 11. 1 11. 3 8. 8 (1H- 1. 4 0. 4 gg 2 i i H 0. 2 Trace 391% 10. s 8.4 12. 5 1a. 4 13. 5 8.0 7.1 e. 7 Oil54. 7 59. 9 46. 1 40. 1 33. 1 35. 1 36. 3 38. 5

1 Control.

Norn.Reaction gas temperature is approximately 80 0. lower than furnacetemperature.

These data clearly demonstrate that use of a hydrogen sulfide precursorsuch as ammonium sulfide improves the yield of propylene as compared tocontrol runs wherein a hydrogen sulfide precursor is not employed.

EXAMPLE 2 The runs of Example 1 are repeated except that an equivalentamount of hydrogen sulfide is employed in lieu of the hydrogen sulfideprecursor, ammonium sulfide. Similar results are obtained.

EXAMPLE 3 The runs of Example 1 are repeated except that no steam isemployed, a pressure of 65 p.s.i.g. is employed, a residence time of0.25 second is employed, a temperature of 2000 F. is employed, and 35parts by weight of H 8 per 100 parts by weight of naphtha are employed.Similar results are obtained to those of Example 1.

We claim:

1. In a process for cracking naphtha having a boiling range of 90 F. to400 F. and a specific gravity of 0.65 to 0.78 to alkenes and alkanes,the improvement comprising admixing about 2.0 to about 20 parts byweight of H 8, or an amount of a compound which yields an SH radical inthe cracking environment sufficient to yield that amount of H 8, per 100parts by weight of naphtha and H 8, or the precursor thereof, in themixture comprising H S, or the precursor thereof, and the naphtha to becracked and then passing the resulting mixture through a reactormaintained at a temperature of about 1300 to 1800" F. with a residencetime of 0.25 to 2.0 seconds and a pressure of 0 to 65 p.s.i.g., andwherein 0.5 to 0.75 pound of steam per pound of naphtha is charged tothe reactor, said improvement providing an increase in selectivity ofpropylene in the al'kenes.

2. The improved process of claim 1 wherein the naphtha is a petroleumderived naphtha.

3. The improved process of claim 2 wherein CS or (NH S is employed as anH 5 precursor.

4. The improved process of claim 1 wherein H 8 is employed per se.

5. The improved process of claim 1 wherein the cracking reaction iscarried out continuously; and wherein the reaction is carried out at agas hourly space velocity of about 400 to 22,000 cc. of gaseous feedvolume per cc. of reactor volume per hour at standard temperature andpressure; and wherein the temperature is 1400 F. to 1700 F.

6. The improved process of claim 1 wherein CS or (NHQ S is employed asan H S precursor.

7. The improved process of the claim 1 wherein H 8 is employed per se.

References Cited UNITED STATES PATENTS 2,415,477 2/1947 Folkins et a1260-683 2,361,149 10/1944 Perquin 208106 2,168,840 8/1939 Groll 260683.33,641,190 2/1972 Kivlen et a1. 260683 DELBERT E. GANTZ, Primary ExaminerC. E. SPRESSER, JR., Assistant Examiner US. Cl. X.R.

